The skin, mucous membranes, hair and/or nails constitute a physical barrier between the organism and its environment. The skin is composed of two tissues: the epidermis and the dermis. The epidermis is the outermost layer of the skin which is impermeable and therefore provides protection from external agents. It is a keratinized pluristratified epithelium which is continually renewing itself. Keratinocytes constitute the principal population of cells in the epidermis and are responsible for maintaining the epithelial structure due to their function as a barrier.
The epidermis is composed of several cell layers; basal stratum which is the deepest layer connected to the dermis in the dermal-epidermal union and is composed of undifferentiated cells. Over time, these cells differentiate and migrate towards the surface of the epidermis, constituting the different layers. The uppermost layer formed is the stratum corneum which is composed by the corneocytes. The corneocytes are keratin-rich cells which are capable of retaining water, and are surrounded by a protein and a lipid shell. There are from 10 to 30 layers of stacked corneocytes, which are connected to each other by protein bridges called desmosomes. The resulting structure is a natural physical barrier of skin which retains water. Corneocytes are dead cells which are eliminated by desquamation, and which, in the absence of water, do not desquamate normally leading to a dense, dry and rough skin appearance. The loss of the superficial stratum caused by desquamation is compensated by the migration of cells from the basal stratum towards the surface of the epidermis. This is, therefore, a process of continual renewal of the skin which helps to keep it soft.
The corneocytes contain a protein called filaggrin which binds to keratin proteins. Filaggrin is located in the outer part of the corneocytes, whilst keratin, which is capable of retaining water, remains in the inner part of the corneocytes. When the humidity content of the skin decreases, specific proteolytic enzymes of the corneum stratum cause the rupture of filaggrin in free amino acids in order to control the osmotic pressure of the skin and the quantity of water that it contains. All these free amino acids are produced together with other physiological chemical products such as lactic acid, pyrrolidone, carboxylic acids, urea and other salts present in the corneum stratum, called “natural hydration factors” which are responsible for maintaining the skin moist and flexible by attracting and retaining water. The content of water in the corneum stratum under physiological conditions is normally close to 30%. The “natural hydration factors” are water soluble intercellular substances that undesirably can easily leave the skin thus decreasing its concentration, which leads to water not being so easily bound in the epidermis.
The dermis is the layer of skin located under the epidermis and firmly connected to it. It is an elastic support tissue of mesodermal origin which is mainly constituted of fibroblasts and an extracellular matrix of fibrous proteins (collagen and elastin) and non-fibrous proteins (proteoglycans and glycoproteins). The dermis, which is essentially rich in hyaluronic acid and polysaccharides, works as a reserve of water, retaining the water brought to it by the blood vessels. It stores water like a sponge and passes water to the epidermis when is needed, together with other the nutritional substances the epidermis may also need. Therefore, the dermis plays a fundamental role in the development and differentiation of the epidermis. The fibroblasts and the extracellular matrix also influence on the mechanical properties of the skin, in particular, its elasticity, tone and firmness, as well as the skin's density.
The skin can lose water in two ways: mainly through transpiration, which is an active phenomenon caused by the sweat glands to regulate the temperature of the skin, and also, although minimally, by passive evaporation of water through the epidermis. This passive evaporation or insensible water loss takes place with a kinetics that is the reflection of a balance between the water content of the epidermis and the relative humidity of the surroundings, and its measurement is the reflection of the integrity of the skin's barrier. For example, in normal conditions insensible water loss is usually 5 g/m2/hour but in atopic children, and in areas of dry skin without eczema insensible water loss can reach 13 to 18 g/m2/hour.
The integrity of the skin's barrier or the skin's barrier function also depends on the density of the corneum stratum. The corneum stratum has been compared to a brick wall in which the keratinocytes or corneocytes (bricks) are the essentially protein non-continuous portion, terminally differentiated, which are embedded in a continuous matrix of specialized lipids (mortar). The lipids provide the essential element of the barrier to water, and the corneocytes protect against continual abrasion by chemical or physical injuries.
Hydration is an essential factor in the maintenance of the skin's youthfulness and vitality for any age group. When the quantity of water is insufficient, the stratum corneum loses elasticity and experiences a sensation of tightness, a phenomenon which is usually referred to with the term “dry skin”. However, properly hydrated skin is soft, flexible and has a young, glowing look.
Healthy skin is that which maintains ideal water concentration levels. The presence of water in the dermis and epidermis favors the group of regenerative mitotic reactions of the cutaneous cells, which contribute to the regeneration of our skin. An optimal water concentration is decisive for the flexibility of the skin and, as a consequence, for the prevention of the appearance of wrinkles caused by age and their treatment, and for the healing of small wounds.
However, homeostasis of the skin can be affected by certain physiological factors (age, menopause, hormonal changes, lack of nourishment and lack of hydration, xerosis, etc.) or environmental factors (ultraviolet radiation, pollution, stress, hypoxia, infectious agents, dry weather conditions, irritants, etc.). These factors cause the decrease of an assimilation and fixation of water in the skin which quickly becomes obvious on the cutaneous surface through unmistakable signs such as dry skin or a tendency to irritation. This leads to a decrease in the regeneration of the epidermis (the cells in the basal stratum are less actively divided, the proteins in the skin are denatured and disrupted, and/or the protective intercellular lipid layers are eliminated and cohesion between the cells is reduced) which leads to a decrease in the skin's hydration. Environmental factors also cause deregulation of the hair and nails' hydration, both becoming rough, fragile and brittle.
The cosmetic and dermopharmaceutical industry has undertaken considerable efforts to develop compounds which are capable of maintaining the water balance of the skin, mucous membranes, hair and/or nails, with the objective of improving its appearance, as well as its protective function and function as a barrier. One of these ingredients is hyaluronic acid; an unsulfated glycosaminoglycan of the extracellular matrix formed by D-glucuronic acid and D-N-acetylglucosamine. Hyaluronic acid is capable of retaining water in the skin, helping to maintain the skin more hydrated, elastic and with a more uniform cutaneous surface. The amount of hyaluronic acid which synthesizes the skin drastically reduces with age (Matuoka et al. Aging, 1989, 1(1):47-54) and this is the cause of the tendency of mature skin to dry out, to lose elasticity and to form wrinkles. Hyaluronic acid plays an important function in the prevention and decrease both wrinkles and expression lines; one of the more commonly employed strategies by the cosmetic and dermopharmaceutical industry for the treatment of wrinkles is the administration of hyaluronic acid both topically and subcutaneously due to its capacity of water absorption and therefore fill the wrinkle from inside the skin.
Hyaluronic acid is found in the extracellular matrix of human and animal tissues, but it also exists in certain strains of bacteria such as those of the genus Streptococcus and Pasteurella, which produce it by emulating animal tissues as a way of protecting themselves against attack from the immune system of the animals they infect, as they are pathogenic microorganisms. Therefore, the production of hyaluronic acid is possible from the fermentation of bacteria which produce it naturally. In addition to this, it should be noted that its production is also possible through other genetically modified bacteria.
In the same way that certain bacteria produce hyaluronic acid, there are also bacteria which can produce other sugar or exopolysaccharide polymers. The existence of exopolysaccharides has been known since the 1970s, they are produced by species of bacteria which live in ecosystems known for their extreme conditions. The production of exopolysaccharides by the bacteria which live in these ecosystems is principally related to functions of survival (Raguénès et al. J Appl Microbiol., 1997 April, 82(4):422-30).
Different exopolysaccharides described in the prior art which have been used for cosmetic and/or dermopharmaceutical purposes, such as the exopolysaccharide produced by a strain of bacteria of the genus Pseudomonas described in patent EP0534855 B1 which is used as a thickening, gelling and/or texturizing agent. Besides, the patent application FR2871476A1 describes the GY785 strain of hydrothermal origin of the genus Alteromonas which produces an exopolysaccharide that can be used as a healing agent; patent EP0987010B1 describes an exopolysaccharide produced by a mesophilic bacterium of hydrothermal origin which improves the skin's defense system and patent application US2010/009931 describes the exopolysaccharide produced by a microalgae strain of the genus Porphyridium as a tensing agent, also improving the firmness, elasticity and tonicity of the skin. The American patent application US2009/069213A1 also describes the microalgae strain Porphyridium sp. that produces a polysaccharide which presents anti-wrinkle and hydrating properties. U.S. Pat. No. 6,344,346B1 also describes cosmetic compositions with hydrating properties caused by a polysaccharide of natural origin excreted by a bacterium of the genus Rhizobium. 
Another exopolysaccharide which has proven to have numerous advantageous properties for the skin is the exopolysaccharide described in application WO2009/127057, produced by strains of the bacterial species Staphylococcus epidermidis and Staphylococcus aureus. After applying a cosmetic composition of this exopolysaccharide the hydration and the morphology of the corneum extract improves, and the desquamation of the skin occurs.
Finally, patent application JP2003-313131 should also be mentioned since it describes a polysaccharide sulfate produced by a strain of Alteromonas sp. SN-1009 (FERM BP-5747) with anti-wrinkle properties.
Surprisingly the applicant of this invention has found a new alternative to the exopolysaccharides described in the prior art based on a new exopolysaccharide excreted by the non-hydrothermal bacterial strain Pseudoalteromonas sp., deposited with the CNCM under number I-4150 according to the Budapest Treaty, which improves the hydration of the skin, mucous membranes, hair and/or nails and prevents and/or reduces wrinkles.